Ion source for calutrons



g- 16, 1955 E. o. LAWRENCE 2,715,682

ION SOURCE FOR CALUTRONS Filed Feb. 3, 1945 4 Sheets-Sheet l HEATER SUPPLY F/LAME/VT SUPPLY 2 ARC SUPPLY ACCELERA TING ELECTRODE SUPPLY Fig.1

10 28b /4 zsgz z z u zr 2 WW I W WW4 l6 7 L" f mamsr/q FIELD 24bW V V W% M Q L9 INVENTOR.

ERNEST 0. LAWRENCE dMdufim/n AITORNEY 6, 1955 E. o. LAWRENCE 2,715,682

ION SOURCE FOR CALUTRONS Filed Feb. 3, 1945 4 Sheets-Sheet 2 26 22 26 65c 24b 65b 65a INVENTOR. ERNEST O. LAWRENCE ATTORNEY Aug. 16, 1955 E. o. LAWRENCE 2,715,682

IQN SOURCE FOR CALUTRONS Filed Feb. 3, 1945 4 Sheets-Sheet 3 Fig. 5

I N VEN TOR.

ERNES T 0. LA WRENC E ATTORNEY 6, 1955 1 E. o. LAWRENCE 2,715,682

ION SOURCE FOR CALUTRONS Filed Feb. 3, 1945 4 Sheets-Sheet 4 F a a 93 HEATER SUPPLY F/LAMENT SUPPLY ARC SUPPLY ACCELERA TING ELECTRODE SUPPLY Fig.7

IN VEN TOR. ERNEST O. LAWRENCE ATTORNEY United States Patent Ofi ice 2,715,682 Patented Aug. 16, 1955 IGN SOURCE FOR CALUTRONS Ernest 0. Lawrence, Berkeley, Calif., assignor to the United States of America as represented by the United States Atomic Energy Commission Application February 3, 1945, Serial No. 576,123

8 Claims. (Cl. 250-413) This invention relates to improvements in electric discharge devices, and more particularly to calutrons of the type disclosed in my copending applications, Serial No. 557,784, filed October 9, .1944, and Serial No. 536,401. filed May 19, 1944.

A calutron is a device for increasing the proportion of a selected isotope in an element containing a plurality of isotypes in order to produce the element enriched with the selected isotope. Such a calutron essentially comprises means for vaporizing a quantity of material containing the element that is to be enriched with the selected isotope; means for subjecting the vapor to ionization, whereby at least a portion of the vapor is ionized, so that ions of the different isotypes are produced; electrical means for segregating the ions from the un-ionized vapor and for accelerating the segregated ions to relatively high velocities; magnetic means for deflecting the ions along curved paths, the radii of curvature of the paths of the ions being proportional to the square roots of the masses of the ions, whereby the ions are concentrated in accordance with their masses; and means for deionizing and collecting the ions of the selected isotype thus concentrated, thereby to produce a deposit of the element enriched with the selected isotope.

The apparatus is especially useful in producing uranium enriched with U 1n the previously-mentioned copending application, Serial No. 536,401, there is disclosed a calutron of the multiple beam type, including, as shown in Figures 24, 25, and 26 thereof, an ion source unit provided with an arc block having a number of arc chambers .formed therein. In this source unit, each arc chamber is provided with electron emitting structure individual thereto which is utilized to ionize the vapor contained in the associated arc chamber.

Likewise, the instant application pertains to a calutron of the multiple beam type including an ion source unit provided with an arc block having a number of arc chambers formed therein. In this source unit, however, the arc chambers are provided withelectron emitting structure common to all of them that is utilized to ionize the vapor contained in the associated arcchambers. In another aspect, two or more electron emitting devices may be combined electrically in such manner as to reduce the total number of electrical leads.

One object of this invention is to provide .in a calutron ion source unit, an improved cathode arrangement that is efiicient in operation.

Another object of the invention -is to provide a calutron ion source unit with-cathode structure requiring a reduced number of electrical leads connected thereto.

Another object of the invention is to provide in a calutron ion source unit including a cathode, animproved arrangement for controlling the ratio between the emissions "of a plurality of portions of the cathode.

Another object of "the invention is to provide a calutron ion source unit with an improved arrangement utiliz- III ing a single cathode to produce a plurality of are discharges.

A further object of the invention is to provide a calutron ion source unit with improved cathode structure utilizing a multi-phase source of power.

Further objects of the invention will appear from a reading of the following detailed description of apparatus embodying the invention.

In the accompanying drawings, forming part of the specification,

Fig. 1 is a diagrammatic plan view of a calutron comprising an improved ion source unit;

Fig. 2 is a vertical sectional view of the calutron taken along the line 22 of Fig. 1;

Fig. 3 is a vertical sectional view of the ion source unit incorporated in the calutron shown in Fig. 1 and taken along the line 3-3 in Fig. 6;

Fig. 4 is a front view of the ion source unit taken along the line 44 in Fig. 3;

Fig. 5 is a fragmentary plan view of the ion source unit;

Fig. 6 is a horizontal sectional view of the ion source unit, taken along the line 6-6 in Fig. 3;

Fig. 7 is a fragmentary diagrammatic plan view, similar to Fig. l, of a calutron comprising a source unit including a modified cathode arrangement; and

Fig. 8 is a plan View, similar to Fig. 5, of an ion source unit including a cathode of modified structure, which may be incorporated in either of the calutrons shown in Figs. 1 and 7.

Referring now more particularly to Figs. 1 and 2, there is illustrated a calutron 10 comprising magnetic field structure, including upper and lower pole pieces 11 and 12 provided with substantially parallel spaced-apart :pole faces, and a tank 13 disposed between the pole faces of the pole pieces 11 and 12. The pole pieces 11 and 12 carry windings, not shown, which are adapted to be energized in order to produce a substantially uniform and relatively strong magnetic field therebetween, which magnetic field passes through the tank 13 and the variousparts housed therein. The tank 13 is of tubular configuration,- being substantially arcuate in plan, and comprising substantially fiat parallel spaced-apart top and bottom walls 14 and 15, upstanding curved inner and outer side walls '16 and 17, and end walls 18 and 19. The end walls 18 and 19 close the opposite ends of the tubular tank 13 and are adapted to be removably secured in place, whereby the tank 13 is hermetically sealed. Also, vacuum pumping apparatus 13a is associated with the tank 13, whereby the interior of the tank 13 may be evacuated to a pressure of the order of 10-- to 10- mm. Hg. Preferably, the component parts of the tank 13 are formed of steel, the top and bottom walls 14 and 15 thereof being spaced a short distance fromthe pole faces of the upper and lower pole pieces 11 and 12 respectively, the tank 13 being retained in such position in any suitable manner, whereby the top and bottom walls 14 and 15 constitute in'effect pole pieces with respect to the interior of the tank 13, as explained more fully hereinafter.

The removable end wall 18 suitably supports an ion source unit 20 comprising a charge receptacle 21 and a communicating arc-block 22. An electric heater 23 is arranged in ,heat exchange relation with the charge receptacle 21 and is adapted to be connected to a suitable source ofheater supply, whereby the charge receptacle 21.

' maybe appropriately heated, the charge receptacle 21 being formed of stainless steel or the like. The arc-block 22 is formed, at least partially, of brass or the like and has a plurality of upstanding slots formed in the front wall thereof remote from the charge receptacle 21. By way of example, two such slots 24a and 241) are shown, but it is understood that more than two may be employed. Thus, the arc-block 22 is of hollow construction, the

filament current source through the resistor 32.

cavity therein communicating with the interior of the A charge receptacle 21. 1

Also, the removable end wall 18 carries a filamentary cathode having electron emitting portions 25a'and 25b adapted to be'connected to a suitable source of filament supply, the filamentary cathode overhanging the upper end of the arc-block 22 and arranged in alignment with respect to the upper end of the cavity formed therein.'

7 7 unit 20, which in turn is connected to the positive terminal of a suitable source of accelerating electrode supply, as explained more fully hereinafter. On the other hand, the tank 13 is grounded. Also, the-filamentary cathode electron emitting portions 25a and 25b and the cooperat ing anode 26 are adapted to be connected to a suitable source of arc supply. The electron emitting portions 25a and 25b of the cathode are connected by three conductors 29, 30 and '31 to the potentiometer 33 and the resistance element of the potentiometer 33 is connected across the The common'terrninal of the cathode portions 250 and-25b is.connected to the variable contactor of the potentiometer 33 by the conductor 30 for the purpose of varying the proportion of the cathode current flowing in the elec tron emitting-portions 25a and 25b for the purpose explained more fully hereinafter.

Further, the removable end wall IS carries. ion ac-- celerating structure 34, formed at least partially of tungthe collector block 36 constitutes an electrostatic shield for the high-velocity ions traversing the curved paths between the slits 35a and 35b formed in the ion accelerating structure 34 and the slots 41, 42, 43, and 44 formed in the collector block 36, as explained more fully hereinafter.

Considering now the general principle of operation of the calutron 10, a charge comprising a compound of the element to be treated is placed in the charge receptacle 21, the compound of the element mentioned being one which may be readily vaporized. The end walls 18 and 19 are securely attached to the openends of the tank 13,

whereby the tank 13 is hermetically sealed. The various electrical connections are completed and operation of the vacuum pumping apparatus 13a associated with the tank 13 is initiated. 'When a pressure of the order of 10- to 1 3- mm. Hg is established within the tank 13, the electric circuits for the windings, not shown, associated wtih the pole pieces 11 and 12.are closed and adjusted, wherebya predetermined magnetic field is established therebe tween traversing the tank 13. The electric circuit 'for the heater 23 is closed, whereby the charge in the charge re ceptacle 21 is heated and vaporized. The vapor fills the l charge receptacle 21 'and is conducted into the cornmunicating cavity formed in the arc-block 22. The'electric circuits for the filamentary cathode electron emitting sections 25a and 25b are closed, whereby the filamentary cathodes are heated and rendered electron emissive.

1 Then the electric circuit between the filamentary cathode electron emitting sections or portions 2511' and 25b and the anode 26 is closed, whereby an arc discharge is struck therebetween, electron streams proceeding from the filamentary cathode electron emitting sections 25a and 25b 3 through the collimating slots 28a and 28b formed in the [the contactor of the potentiometer. 33 increases the cur sten or the like, and disposed in spaced-apart relation with respect to the wall of the arc-block 22 in which the slots 24a and 24b are formed. More specifically,two slits 35a and 355 are formed in the ion accelerating structure 34 and these are arranged in substantial alignment with respect to the slots 24a and 24b, respectively, formed in the wall of .the'arc-block 22. The source of accelerating electrodesupply is adapted to be connected between the arcblock 22 and the ion'accelerating structure 34, the posi-- tive and negative terminals of the supply mentioned being respectively connected to the arc-block 22 a nd to the ion accelerating structure 34. Further, the negative terminal of the ion accelerating electrode supply is grounded.

. vThe removable end Wall 19 suitably supports an ion collector. block 36 formed of stainless steel or'the like ,-and

provided with four laterally spaced-apart cavities of pockets'37, 38, 39, and 40 which respectively communicate with four aligned slots 41, 42, 43, -and'44 formed in all) the wallof the collector block 36 disposed remote from I the -r'emovableend 'wall .19. It is noted that the pockets 39'and 40 are adapted to receive two constituent isotopes of anelement which have been separated in the calutron 10 and projected. through one slot 24a in the arciblock V 22, as explained 'more'fully hereinafter, and that the 7 pockets 37.and 38 are similarly adapted to receive two constituent isotopes which have been projected through the other slot 24b in the arc block 22. Finally,the collector block 36 is electrically'connected to the ion accelterrninal of the accelerating electrode supply; while the tank 13, the Jion accelerating structure 34 and the col lector block 36 are connected'to the negativev grounded terminal of the accelerating electrode supply; the source unit 20 being electrically insulated from the component parts of the tank13. Thus'the portion of the tank ;13

disposed between the ion accelerating structure 34 and crating structure 34. Thus it will be understood that the a V source unit20'is connected to the positive ungrounded collimating electrode 27 to the anode 26'and these electron streams may be controlled in intensity by moving the variable contractor of the potentiometer 33. Moving rent through one of the cathode electron emitting sections and decreases the current through the other electron emit ting section thereby'controlling theintensitie's of the elec tron streams through the collirna ting slots. The collimating slots 28a and 285 formed'in the collimating electrode 27 define the cross-sections of the 'strearns of electrons proceeding into the arc-block 22, whereby each arc discharge has a ribbon-like configuration and breaks up the molecular 'form of the compound of thevapor to a considerable extent, producing positive ions of the element that is to be enriched with the selected one of "its isotopes.

The electric circuit' between the farc block 22 and'the ion accelerating structurej34, i's completed, the ion accel crating structure'34 being at a high negative potential with respect to the arc-block 22, wherebythe positive ions in the arc-block 22' "are" attracted 'by' the ion accelerating "structure'34 and' accelerated through the voltage im-.

pressed therebetwe en; More particularly, the positive ions'proceed from the cavity formed'in the arc-block 22 through the slots 24c; 'and24b' formed .inthe wall'thereof, and acrossfthe space betweenthe ion accelerating structure 34 and the adjacent wallbf the arc-block 22', V

and thence through'the slits 35 z'and 35b formed in the ion accelerating structure'34. The high-velocity positive 7 3 ions form two vertical upstanding ribbons 'o'r beams pro ceeding fromthe cavity formed in' the arc-block "22 through the two'slots'24a and24b and the two aligned slits35a and 35b respectively p p e As previously'noted,the collector block 36,-as well as the tank 13,- iselectrically connected to the ion accelerating structure 34, whereby there is an electricfield-free path for the high-velocity positive ions disposed between the ion accelerating structure 34 and the collector block 36 'within the tank 13. The high-velocity positive ions are deflected from their normal straightline path and from a vertical. plane passing through the slots 24a and 24b and. the aligned slits 35a and 35b,

due to the effect of the relatively strong magnetic field maintained through the space within the tank 13 through which the positive ions travel, whereby the positive ions describe arcs, the radii of which are proportional to the square roots of the masses of the ions and consequently of the isotopes of the element mentioned. Thus, ions of the relatively light isotope of the element describe interior arcs of relatively short radius and are focused through the slots 41 and 43 into the pockets 37 and 39 formed in the collector block 36; whereas ions of the relatively heavy isotope of the element describe exterior arcs of relatively long radius and are focused through the slots 42 and 44 into the pockets 38 and 40 formed in the collector block 36. Accordingly, the ions of the relatively light isotope of the element are collected in the pockets 37 and 39 and are de-ionized to produce a deposit of the relatively light isotope of the element therein; while the ions of the relatively heavy isotope of the element are collected in the pockets 33 and 40 and are de-ionized to produce a deposit of the relatively heavy isotope of the element therein.

After all of the charge in the charge receptacle 21 has been vaporized, all of the electric circuits are interrupted and the end wall 18 is removed so that another charge may be placed in the charge receptacle 21 and subsequently vaporized in the manner explained above. After a suitable number of charges have been vaporized in order to obtain appropriate deposits of the isotope of the element in the pockets 37, 38, 39, and 40 of the collector block 36, the end wall 19 is removed and the deposits of the collected isotopes in the pockets 37, 38, 39, and 40 in the collector block 36 are reclaimed.

Of course, it will be understood that the various dimensions of the parts of the calutron 10, the various electrical potentials applied between the various electrical parts thereof, as well as the strength of the magnetic field between the pole pieces 11 and 12, are suitably correlated with respect to one another, depending upon the mass numbers of the several isotopes of the element which is to be treated therein. In this connection reference is again made to the previously-mentioned copending application, Serial No. 557,784, filed October 9, 1944, for a complete specification of a calutron especially designed for the production of uranium enriched with the isotope U By Way of illustration, it is noted that when the calutron is employed in order to produce uranium enriched with U the compound of uranium which is suggested as a suitable charge in the charge receptacle 21 is UCl4, as this compound may be readily vaporized and the molecular form of the vapor may be readily broken up to form positive ions of uranium. In this case, uranium enriched with U is collected in the pockets 37 and 39 of the collector block 36, and uranium comprising principally U is collected in the pockets 38 and 40 of the collector block 36. Also, it is noted that from a practical standpoint, the deposit of uranium collected in the pockets 37 and 39 of the collector block 36 contains considerable amounts of U in view of the fact that this isotope comprises the dominant constituent of normal uranium. Furthermore, the deposit of uranium collected in the pockets 37 and 39 of the collector block 36 contains a considerably increased amount of U in view of the fact that it is not ordinarily feasible to separate U and U in the production of relatively large quantities of uranium enriched with U for commercial purposes. Accordingly, in this example the uranium deposited in the pockets 37 and 39 of the collector block 36 is considerably enriched, both with respect to U and U and considerably impoverished with respect to U as compared with natural or normal uranium.

Referring now more particularly to Figs. 3 to 6, inelusive, of the drawings, there are illustrated the structural details of the ion source unit 20 which is arranged in the magnetic field between the pole pieces of the calutron in the manner previouslyexplained, the source unit comprising the charge receptacle 21 and the arc-block 22. The charge receptacle 21 comprises wall structure, including a removable cover 59, defining an upstanding cavity 51 therein, that is adapted to receive a removable charge bottle 52 containing a charge 53 which is to be vaporized. The arc-block 22 comprises wall structure defining an upstanding distributing chamber 54 and two upstanding arc chambers 55a and 55b therein, the cavity 51 communicating with the distributing chamber 54 through a tubular member 56 supported by the wall structure of the charge receptacle 21 and the wall structure of the arc-block 22. The wall structure of the charge receptacle 21 has two upstanding cavities 57 formed therein, in which two elements of the electric heater 23 are arranged. Preferably, each element of the electric heater 23 comprises a coil of resistance Wire wound on a supporting insulator, as indicated, whereby each element of the electric heater 23 may be independently placed in and removed from the associated cavity 57. Thus, the charge receptacle 21, and consequently the charge bottle 52, may be appropriately heated in order to vaporize the charge 53 contained in the charge bottle 52. Similarly, the arcblock 22 has two up-standing cavities 53 formed therein, in which two electric heating elements 59 are arranged. Preferably, each of the electric heating elements 59 comprises a coil of resistance Wire wound on a supporting insulator, as indicated, whereby each of the electric heating elements 59 may be independently placed in and removed from the associated cavity 58. Thus, the arcblock 22, and more particularly the distributing chamber 54 therein, may be heated in order to prevent condensation of the contained vapor, as explained more fully hereinafter.

More particularly, the wall structure of the charge receptacle 2i is formed of copper or brass; and the wall structure of the arcblock 22 is formed of copper or brass and comprises two primary members 60 and 61. The distributing chamber 54 and the cavities 58 are formed in the member 6%; while the arc chambers 55a and 55b are formed in the member 61, a series of longitudinally spaced-apart openings 62a and 621) are formed in the wall of the member 61 and communicate between the arc chambers 55a and 55b and laterally extending manifold passages 62, also formed in the wall of the member 61, the manifold passages 62 communicating with the distributing chamber 54. Also, the arc-block 22 comprises a front plate 63 formed of copper or brass and secured to the member 61; the source unit 2 5 being supported by two rearwardly extending arms 64 which are secured to the member 61 and the front plate 63.

Upstanding strips 65a, 65b and 65c, formed of tungsten or the like, are secured to the member 61 adjacent the arc chambers 55a and 55b, thereby to define upstanding slots therebetween communicating with the arc chamhers 55a and 55b. Also, upstanding strips 66a, 66b and 66c, formed of tungsten or the like, are secured to the front plate 63 adjacent the strips 65a, 65b and 650 respectively and spaced a small distance forwardly with respect thereto, thereby to define upstanding slots communicating with the arc chambers 55a and 55b. Thus, the slots defined between the strips 65a, 65b and 650 and the slots defined between the strips 66a, 66b and 66c constitute the upstanding slots 24.5; and 24b formed in the front wall of the arc-block 22 and communicating with the arc charnhers 55a and 5517, respectively.

The filamentary cathode comprises two structurally separate U-shaped members 25a and 25b which are carried by a cathode support 67 arranged in cooperating relation with respect to the arc-block 22. The central portions of the cathode elements 25a and 25b overhang the central portions of the arc chambers 55:: and 55b, respectively, with which they are associated; and the collimating electrode 27 is secured to the top wall of the arc-block 22, the collimating electrode 27 having the transverse slots 28a and 28b formed therein, as previously noted, and communicating with the arc chambers 55:: and 55b respectively. More particularly, the cathode elements 251:

' and b are spaced a short distance above the collimating end of the arc chambers 55a and 55b, and in alignment with the cathode elements 25a and 25b and the transverse slots 28a and 28b formed in the collimating electrode 27 V .The cathode support 67 includes three terminals 68, 69,

and 70, which are connected to the three conductors 29, 3 0, and 31 by the respective conductors 71, 72, and 73. The adjacent legs of the cathode members 25;! and 25!;

' are removably clamped to the middle terminal 69 by a number of clamping screws 74 or the like, while the out- 'side legs of the cathode members 25a and 2511 are remov- =ably clampedto the respective terminals 68 and 7a) in a similar manner.

It will be understood, therefore, that threesconductors will sufiice. to supply electrical energy to the, two cathode members 25a and 25b. The negative and positive terminals of the arc supply are respectively connected to the filamentary cathode members 25a and 25b and to the arc-block 22, the anode 26 and the collimating electrode 27 being connected together by the arc-block 22 and consequently to the positive terminal of i the arc supply mentioned, as previously noted.

Further, the ion accelerating structure 34' comprises three upstanding strips 76, 77, and 78 disposed forwardly of the strips 66a, 66b and 660, respectively, and secured to two transversely-extending top and bottom members 7 9 and 80 to form a unitary structure. The three strips 76, 77, and 7 8 are arr'anged in transverse spaced-apart relation and carry four electrodes 81, 82, 83, and 84, formed of tungsten or the like, the middle strip '77 carrying two electrodes 82 and 83, one on each side. The four elec: trodes 81, 82, 83, and 84 are arranged in transverse spaced-apart relation to define two upstanding slits 35a and 35b therebetween, and arranged in alignment with the slots 24a and 24b formed in the front wall of the arc-block 22.

As previously noted, the ion accelerating structure 34, together with the source unit 20, is supported by the removable end wall 18 of the calutron 10, and the positive and negative terminals of the accelerating electrode supply are respectively connected to the arc-block 22 and the 7 ion accelerating structure 34. Finally, upstanding semicircular bafiie plates 85a and 85b, formed of quartz or the like, are arranged in the arc chambers a and 55b, re

spectively, and a series of longitudinally spaced-apart openings 86 is formed in each of these baflle plates.

7 Considering now the detailed operation of the ion' source unit 20, when the electric circuit for the heater 23 is completed, the charge receptacle 21 and consequently thecharge bottle 52 are heated, whereby the charge 53 is vaporized, filling the cavity in the charge bottle 52.

The vapor passes through the tubular member 56 into the distributing chamber 54, wherebythis chamber is filled with the vapor. The vapor is distributed in the distributing chamber 54 and passes through the laterally extending manifold passages 62 and the openings 62a and 62b formed in the wall of. the member 61 into the rear 7 part of the arc chambers 55a and 55b. The vapor then passes through the openings 86 formed in the baflle plates 7 85a and 85b into the front parts of the arc chambers 55a and 55b, whereby these parts'of the arc chambers are filled with the vapor. More particularly, the arc 8 when the arc supply circuit is completed between the filamentary cathode elements 25a and 25b and the arcblock 22, electrons are projected from the central portions of the filamentary cathode elements 25a and 25b toward the collimating electrode 27. More particularly, some of these electrons pass through the two transverse 'slots 28a and 28b formed in the collimating electrode 27,

into the arc chambers 55aand 55b, and proceedtoward the anode 26. Accordingly, thescollimating electrode 27 causes two streams of electrons having ribbon-like configurations in the shape of theslots 28a and 28b respectively to be projected into the arc chambers 55a: and 55b,.

whereby thevapor in the arc chambers is ionized and the intensities of these electron streams may be varied by adjusting the variable contactor of the potentiometer 33 so that the ionization of the vapors in the arc chambers 7 may be controlled. When the accelerating electrode supply circuit is completed, the positive ions produced in the arc chambers 55a and 55b are drawn through the two upstanding slots 24a and 24b, formed in the front wall and 25b, which current is of the order of 100 amperes or more, may be controlled by means of the impedance 32. The current in each of the individual cathode members 25a and 25b may be further controlled by means of the potentiometer 33 as described hereinbefore. As a result, the intensity of the electron stream in one are chamber 55a may be made equal to, greater than, or less than that in the other arc chamber 55b,"for the purpose of controlling the ionization in the arc chambers 55 and 55b. 7 a

Referring now to Fig. 7, there is shown a calutron 100 comprising a source unit 21 including the improved cathode arrangement hereinabove described in conjunction with Figs. 1 to 6, inclusive, and also including a modified form of cathode heater supply. More particularly, this arrangement comprises a polyphase transformer 90, in-

cluding a primary winding connected to a suitable source of polyphase alternating current filament supply and a secondary winding connected by way of variable resistors 91, 92, and 93 to three conductors 29, 30, and 31, which in turn are connected to the three terminals 68, 69 and 70 supporting the two filamentary cathodes 25a and 25b. The midtap of the secondary winding of the transformer is connected to the negative terminal of the arc sup:

ply; while the positive terminal of the 'arc supply is connected to the arc block 22, as previously explained.

It will be understood that the operation of the calutron shown in Fig. 7 is substantially identical to that of the calutron 10 shown in Fig; 1; and specifically, when the' filament supply circuit is closed, the filamentary cathodes 25a and 25b are heated by the flow of polyphase current therethrough. Also it will be understood that the division of current between the cathodes 25a and 25b may be suitably controlled by adjusting the resistors 91, 92, and 93 in an obvious manner.

Referring now to Fig. 8, there is shown a modified form of cathode structure 200 which may be employed in the 'ion source unit 20 utilized inthe calutrons 10 and 100,- respectively shown in Figs.- 1 and 7. More particularly;

the cathode 200 is of one-piece construction, having a substantially E shape including three legs201, 202, and 203 and two intermediate electron emitting portions 204 and 205. It will be understood that the legs 201, 202, and 203 are respectively clampedto the terminals 68, 69a, and 70, and'that theemitting portions 204 and 205-are 9 respectively disposed over the two collimating slits formed in the-associated collimating electrode disposed therebelow, or for the purpose previously explained.

In view of the foregoing descriptions of the calutrons 10 and 100 respectively shown in Figs. 1 and 7, it will be understood that the adjustment of the potentiometer 33 to control the division of current between the filamentary cathodes 25a and 25b in thecalutron 10, as well as the adjustment of the resistors 91, 92, and 93 to control the division of current between the filamentary cathodes 25a and 25b, is efiective to control the heating and consequently the temperature of the two cathode sections 25a and 25b in either case. Control of the temperatures of the two cathode sections 25a and 25b is, of course, effective to govern the electron emission therefrom and the consequent arc discharges through the associated arc chambers 55a and 5512, respectively. This control of the arc discharges through the arc chambers 55a and 55b is effective to govern ionization therein, and consequently the intensity of the respective ion beams which are projected from the two arc chambers mentioned.

While the embodiments of the cathode structure have been illustrated in conjunction with an ion source unit comprising an arc block 22 provided with two arc chambers 55a and 551), it will be understood that the arc block may comprise only one are chamber with which the cathode structure is associated; and in this case, the control of the heating of the two sections of the filamentary cathode is effective to control ionization in the corresponding portions of the associated arc chamber, and consequently the intensity from side to side of the ion beam drawn from the arc chamber mentioned.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may be made therein and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. In a calutron, an ion source comprising wall structure defining an arc chamber, an electron emissive cathode operatively associated with said arc chamber and adapted to discharge electrons thereinto, a source of current connected to three spaced-apart points along said cathode, and means for proportioning the potentials applied from said source between said three spaced-apart cathode points in order to control the electron emission of the corresponding intervening portions of said cathode.

2. In a calutron, an ion source comprising wall structure defining an arc chamber, an electron emissive arc cathode adapted to discharge electrons into said chamber, a source of current connected at a plurality of points to said cathode, and means including an adjustable po tentiometer for varying the potentials applied from said source to said cathode points in order to control the electron emission of different portions of said cathode.

3. In a calutron ion source, well structure defining an arc chamber, an E-shaped cathode having a back-portion and three legs projecting therefrom, a current supply connected to said three legs for passing current through said back-portion to heat said back-portion to electron emitting temperature, said back-portion being positioned adjacent to said are chamber to project electrons into said chamber, and control means connected to said three legs for regulating electron emission from sections of said back-portion.

4. In a calutron, an ion source comprising wall structure defining an arc chamber, an electron emissive cathode adapted to discharge electrons into said chamber, a source of polyphase current connected to three spacedapart points along said cathode, and a variable resistor connected to each of said spaced-apart points for varying the potentials applied from said source between the ad- 10 jacent pairs of said cathode points in order to' control the electron emission of different portions of said cath ode.

5 In a calutron, an ion source comprising wall structure defining an arc chamber, an electron emissive cathode adapted to discharge electrons into said chamber, a source of polyphase current connected to said cathode at a plurality of spaced-apart points, and means for varying the potentials applied from said source between the spaced-apart points of said cathode in order to control the electron emission of diiferent portions of said cathode.

6. Apparatus for producing ions of vaporous material comprising a receptacle for the material, wall structure defining a plurality of elongated arc chambers connected to said receptacle by channels extending through the rear walls of said elongated arc chambers so that said vaporous material is fed to said are chambers at a plurality of places and distributed substantially throughout the length of said arc chambers, a pair of electron emitting elements having the adjacent ends thereof connected together to form a common terminal and having the outer ends thereof connected to outer terminals, each of said are chambers having an aperture at an end thereof, said electron emitting elements being positioned adjacent said apertures to project electron streams into the respective arc chambers and to ionize the vaporous material therein, a polyphase current supply source having one of the phases thereof connected to the common terminal of said electron emitting elements and other phases connected to the outer terminals thereof, and current control apparatus connected to said current supply source phases for controlling the current to said electron emitting elements to vary the intensities of the electron streams into said arc chambers.

7. Apparatus for producing ions of vaporous material comprising a receptacle for the material, wall structure defining a plurality of elongated arc chambers connected to said receptacle by channels extending through the rear walls of said elongated arc chambers so that said vaporous material is fed to said are chambers at a plurality of places and distributed throughout the length of said arc chambers, a cathode having a pair of electron emitting sections connections together to a common terminal, each of said arc chambers having an aperture at an end thereof, said electron emitting cathode sections being positioned adjacent said apertures to project electron streams into the respective arc chambers and to ionize the vaporous material therein, current supply means for said cathode, and current control apparatus connected to said current supply means for proportioning the current to said cathode sections to control the intensities of the electron streams into said arc chambers.

8. Apparatus for producing ions of vaporous material comprising a receptacle for the material, wall structure defining a plurality of elongated arc chambers connected to said receptacle by channels extending through the rear walls of said elongated arc chambers so that said vaporous material is fed to said are chambers at a plurality of places and distributed substantially throughout the length of said are chambers, a cathode having a pair of electron emitting sections connected together to a common terminal, each of said are chambers having an aperture at an end thereof, said electron emitting cathode sections being positioned adjacent said apertures to project electron streams into the respective arc chambers and to ionize the vaporous material therein, a polyphase current supply source connected across the terminals of said cathode, and a potentiometer connected across said current supply source, the contactor of said potentiometer being connected to said common cathode terminal for varying the current to said cathode sections to control the intensities of the electron streams into said arc chambers.

(References on following page) References Cited in the file of this patent UNITED STATES PATENTS 12 FOREIGNIATENTS 317,096

OTHER REFERENCES Livingston et al.: Review 7 vol. 10, February 1939.

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Germany May 26, :1921 V Tuve et aL: Physical Review, v01. 48, August 1 1 9 35, 

1. IN A CALUTRON, AN ION SOURCE COMPRISING WALL STRUCTURE DEFINING AN ARC CHAMBER, AN ELECTRON EMISSIVE CATHODE OPERATIVELY ASSOCIATED WITH SAID ARC CHAMBER AND ADAPTED TO DISCHARGE ELECTRONS THEREINTO, A SOURCE OF CURRENT CONNECTED TO THREE SPACED-APART POINTS ALONG SAID CATHODE, AND MEANS FOR PROPORTIONING THE POTENTIALS APPLIED FROM SAID SOURCE BETWEEN SAID SPACED-APART CATHODE POINTS IN ORDER TO CONTROL THE ELECTRON EMISSION 